AF filter

AF is just like the IF filter except it is variable between 540-1700 (540-1600), and the loop stick type is an antenna as well; thus it must be heavily amplified.  The loop stick itself is really an exposed 2Mhz IF transformer; the only reason for the diffrences in the circuit is the fact that this one is tunable by a gang capacitor

If you bought the one from LA-540 http://www.oselectronics.com/ose_p91.htm skip the steps 1, and 2 below and connect as shown; most have the color configuration shown on the side.  (from oselectronics  loopstik data sheet)

Black = ( - GND) Ground directly to Gang cap
White = AF side of gang cap

Red  = RF Output
Green = ( - GND) Ground RF

Modify your loopstick with solid wire so it can be plugged in to the board, don't make the leads to long!

Figuring out the Loopstick (skip step 1, and 2 if your loopstick colors match, or you can tell what wire goes where by looking at the picture)

Make sure you put the loopstick on the ferrite core before testing frequency, this however will need to be slid across the ferrite core; if you got one out of a radio you will need to heat it up with a hot blower, or set it in front of a space heater to melt the wax; (melt it and remove the coil, and make it freely slide across the ferrite).

Unfortunately some Loop sticks are so poorly labeled, and irraticly wound you may not be able to tell their colors or they may be wrong, but I'm going to show you how to figure out what wire goes where.

Step 1, find the two coils on the Loopstick.

Get a multimeter and put it on continuity and find the two coils, they will show zero ohms when you find them.  (If you can tell the longest coil goes to the antenna side of the gang capacitor.)

Step 2, find the short coil

Turn off the power on your circuit, plug in a coil on the loopstick, and put a short wire off the probe from the signal generator along side of the loopstick with tape. (Do not hold it there with your hand!)

Attach a probe off the oscilloscope to the two loopstick wires (gnd. and positive; polarity matters!) of the probe.

Crank the signal generator all the way up and, adjust around 1600 – 2100 there should be a peak, if there is not change the polarity, and if there is still not try another wire.

Once you find the peak ground both the Loop sticks coils (noting the polarity of the coil you just found), and attach the gang capacitor and try to tune the peak from around 1600KHz down to about 540 (it won't be perfect), with the signal generator and oscilloscope; if it doesn't peak (or tune correctly), change the polarity on the af side of the loop or try repeating step 2.

Note : Double check the polarity, sometimes one way works a little better than the other one (The polarity should always be reversed).

Step 3,  Build the circuit, and Attach an oscilloscope to the "Out" side of the RF amp.

Step 4, Tape a short wire (about the length of the coil itself) to the side of the loopstick (do not hold it there with your hand, and make sure you slide the coil on the correct direction, the short part of the coil (between the green and red wires) should be on the edge).

Step 5, Attach a probe from the signal generator to the wire; set it to 540 KHz, and crank the output.

Step 6, Turn the gang to it's lowest point (all the way counter clockwise)

Step 7, Adjust the loopstick by sliding the coil around on the shaft to peak on the scope at about 540KHz, if you bought the Ocean State Electronics one you will need to put a drop of wax on the flat side underneath on the ferrite to keep it from moving around on you.  NOTE: your hand will interfere with the loopsticks frequency.

Step 8, Turn the gang to it's highest point, (all the way over clockwise).

Step 9, Adjust the trimmer on the back of the cap for 1700 (or 1600), and repeat at step 6 until the gang tunes from 540-1700 KHz (540-1600 KHz)

Step 5, Connect the "out" in the circuit to the "RF in" on the mixer and disconnect the six foot antenna, and oscilloscope.

Step 6, Remove the taped wire from the signal generator and with the gang turned all the way down, reapply power

Step 7,  Turn off the signal generator and turn up the voltage regulator untill you just hear static (make sure the volume is up), and find a clear area and adjust IF 300 untill the static is maximized.

Step 8, then adjust all of the IF stages untill they are maximized (you may need to turn down the voltage regulator eventually to keep the circuit from feeding back on itself, and overloading).

If you hear static and your channels come in good (but the strong ones will overload), go to the next step, else check your circuit; if your curcuit "motorboats", or feeds back on itself, you might want to add some extra power coupling caps in different areas.

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